This invention relates generally to dies for flaring and/or coupling pipe ends, and more particularly, to such a flaring die configured to reduce stress concentration at the base of the flange created by the flaring die.
Pipes and tubing are used to carry a variety of fluids, some are liquids and others are gases. These fluids may be under substantial pressures or at standard pressure. Therefore, pipes and tubing are rated according to the fluid pressures which the conduit can carry without rupturing. A particular conduit is considered to be a pipe or tubing depending upon the wall thickness of the conduit, the industry or application in which it is being used, and sometimes upon whether it is plastic or metal. For present purposes and simplicity the term pipe will be used to encompass both pipe and tubing as those terms are used by those skilled in the art.
In hydraulic connections it is quite common to utilize pipes in which the end of the pipe has been flared to form a collar which is placed to abut against a surface of the device to which the pipe is being connected, or against another flared pipe often with a sealing ring between them. In order to create the flared end or collar it is customary to provide a clamping die which is pressed against the pipe to be flared at a specified distance away from the end of the pipe. This die typically will have a gripping surface containing teeth or threads which bite into the exterior surface of the pipe being held. The die is pressed against the end of the pipe to hold the pipe during flaring. The flaring process is usually performed by a flaring machine having an eccentric cone. The eccentric cone is pressed against the end of the pipe and rotated circumferentially about the end of the pipe to form a flare. The flare can be at any angle relative to the side of the pipe. The pipe flaring practice is quite old, but there have been improvements in the flaring tools. An improved flaring tool and method of using the same for forming a transverse collar on the end of the metal pipe is disclosed in U.S. Pat. No. 4,905,492.
A conventional flaring die comprises two members which are clamped over the pipe near the end to be flared. Each die member has a central semi-circular opening which is placed over the pipe to be flared. The die members are clamped together near the end of the pipe which is going to be flared. The opening through the die members is sized such that the pipe is of slightly larger diameter than the opening so that the pipe is rigidly gripped between the die members. When the die is closed, the teeth or threads on the gripping surface bite into the pipe creating a series of cuts or grooves on the outside of the pipe. Also, the die members have an annular beveled portion, angled outwardly from the gripping surface. The end of the pipe to be flared is pressed against the beveled portion by the eccentric cone to create the flare. The angle of the beveled portion determines the angle of the flared portion of the pipe. During flaring a stress concentration is created at the base of the flared portion. Because the threads of the gripping portion extend to the edge of the annular beveled portion there are cuts or grooves near the base of the flared portion. These cuts create stress risers. Prior to the present invention those skilled in the art did not recognize that such stress risers had been created or if they had recognized their existence, such skilled artisans did not understand their significance. This stress concentration negatively affects the life and usefulness of the pipe, and the joint of which the flared end of the pipe is a member.
We observed that certain couplings made with flared pipes failed in a high pressure system. One of the pipes cracked at the base of the flare. We believe that the crack occurred during a pressure spike in the system. Consequently, we saw a need for a flared pipe that would not crack when exposed to pressure spikes. One obvious solution to this problem is to use a thicker pipe or a pipe made from a stronger alloy. Not only are those solutions more expensive, they also are not practical for many applications.
A better solution is to find a way to make a flared pipe having lower stress at the base of the pipe than the same pipe made in the conventional way. A flaring die which is configured to reduce the stress concentration at the base of the flared portion would increase the life of and reduce limitations on the pipe and the joint of which it is a part.
Another problem encountered with conventional flaring dies is positioning the pipe in the die so that the flare is of a desired length. If one simply places the pipe so that the end of the pipe is in the same plane as the face of a conventional die the flare will not extend the full width of the beveled portion. If the pipe extends too far beyond that plane the flare will extend beyond the beveled portion. One solution to the problem is to first determine the correct distance from the end of the pipe where the pipe must be gripped. Then the pipe fitter makes a mark on the pipe at that distance and inserts the pipe into the die until the mark is aligned with the insertion side of the die. Another approach is to make and attach a jig or stop to the die against which the pipe can be placed. Using a jig or stop saves time but adds cost. A better solution would be to design the die to have an alignment guide as part of the die.
We provide a pipe flaring die having a profile configured to reduce stress concentrations at the base of the flared portion of the pipe. The flaring die typically is two arch-shaped members which are clamped around the wall of the pipe to be flared. Each member has a profile which includes a relief area provided between a gripping surface and an annular beveled portion. The gripping surface aids in rigidly holding the pipe while the flared end is formed. The annular beveled portion defines the angle of the flared portion that is created by deforming the end of the pipe outward against the annular beveled portion of the die members. Unlike the dies of the prior art we provide a relatively wide relief area between the gripping surface and the beveled portion. For, example in a flaring die for a two inch pipe the width of the die is 1.625 inches wide, the gripping surface is 0.655 inches wide and the relief area is 0.475 inches wide. Indeed, we prefer that the width of the relief area be about two-thirds of the width of the gripping surface. When a pipe is held by our die the grooves or cuts made in the outer surface of the pipe while the die was gripping the pipe during flaring are spaced apart from the based of the flare. The relief area provides a longer transition distance for the formation of the flared portion. This results in a reduction in the residual stress concentrated in the region of the pipe at the base of the flared portion. Additionally, the edge between the relief area and the annular beveled portion can be provided with a radius which further reduces the residual stress concentration at the base of the flared portion.
We further prefer to provide a recess between the edge of the beveled portion and the face of the die that serves as an alignment guide. The pipe fitter places a ruler or other straight edge across the face of the die and inserts the pipe until the pipe abuts the straight edge.
A further feature according to the invention is that mating surfaces of each die member can be provided with a recessed area that can be externally accessed by a tool to separate the clamped together die members after the flaring process is completed.
Other objects and advantages of the invention will become apparent from a description of certain preferred embodiments shown in the drawings.